In digital computers a common requirement accompanying an adder is to detect the condition when all the sum bits are equal to zero. While not as common, it is sometimes necessary to detect the condition when all the sum bits are equal to the radix less 1, for example, in the binary case when all the sum bits are equal to 1 or in the decimal case when all the sum bits are equal to 9. In the prior art those conditions are found by first performing the addition and then ANDing the result with ZEROS or with NINES or with ONES to determine whether such a sum has been found. Obviously, the detection of such a sum cannot occur until after the summation is complete. Since in many cases the attainment of a sum will complete a machine cycle the further logic operations that are necessary to AND the sum with ZEROS, with NINES or with ONES will take an additional machine cycle and the branch operations which key off the detection will be delayed. It is, therefore, the general object of this invention to eliminte the need of such an additional machine cycle by providing means for detecting a sum of all ZEROS, all ONES, all NINES or indeed of any radix less 1 sum prior to or at least concurrently with the production of the sum. It is an additional object of the invention to incorporate the detection circuits into an adder with carry look-ahead in such a manner that the circuits for generating existing digit functions can be utilized in the detection process.